Phase digitizing system



Feb. 28, 1967 S. G. NEVIUS PHASE DIGITIZING SYSTEM Original Filed Nov.1, 1957 6 Sheets-Sheet S CATHODE K CONTROL GRID G F OCUSING ELECTRODEHIGHVOLTAGE ELECTRODE Al E cos 6 HORIZONAL PLATES VERTlCAL PLATES E sin9 INVENTORv SEARLE 6. NEWS Feb. 28, 1967 s. G. NEVlUS 3,307,105

I PHASE DIGITIZING SYSTEM Original Filed Nov. 1. 1957 6 Sheets'Sheet 4OSCILLATOR E sin (4/? i RESOLVER SEC. 2 SEC.

A ESBMQMOOQ) Em (M N9) X 9 XIO MULTIPLIERS AND E siniQ DETECTORS 0F FIG.L M 3 EsmQ vEsiniMflO 9) DETECTOR DETECTOR GARRY SQGNAL r "num-DiGiTiZEF! DiGiTIZER KNVENTOR. SEARLE G. Nsvms mwmev Feb. 28, 1967 s. G.NEVIUS PHASE DIGITIZING SYSTEM 6 SheetsSheet 5 Original Filed Nov. 1,195'? x 205m om. $924182 &

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Niamey Feb. 28, 1967 s. G. NEVIUS PHASE DIGITIZING SYSTEM 6 Sheets-Sheet6 Original Filed Nov. 1 1957 INVENTOR. SEARLE G. NEVIUS United StatesPatent Office 3,307,105 Patented Feb. 28, 1967 3,307,105 PHASEDI-GITIZING SYSTEM Searle G. Nevius, Tuiunga, Califl, assignor toWhittaker Corporation, a corporation of California 7 Originalapplication Nov. 1, 1957, Ser. No. 693,930. Divided and this applicationMay 28, 1962, Ser. No.

9 Claims. (21. 324-85) tions by using two sine waves having the samefrequency but differing in phase. In such a system one of the sine wavesserves as a reference signal while the other is adjusted to have arelative electrical phase displacement proportional to the physicaldisplacement to be measured.

The electrical phase difference between the two sine waves is measuredby a phase detector circuit which produces signal proportional to theelectrical phase difference. While theoretically this system would seemto work very well, actual practice has shown that variations in the waveform and non-symmetry in the circuits produces an output signal havinginsufficient precision to allow division of a shaft rotation or lineardisplacement into a large number, as for example one hundred thousand,or more, parts, with an accuracy of plus or minus one part, as isdesirable for certain types of research and engineering activities.

The system "of the present invention involves novel phase measuringtechniques and can be used with any one of several different types ofresolvers to provide a satisfactory solution to the foregoing problems.The

electrical phase delay cause by the resolver is transmitted into severalelectrical signal channels with the electrical phase angle beingmultiplied by a different factor in each channel. Each channel isprovided with a phase detector and the D.-C. signal from the phasedetector in each channel is applied to equipment which is used toproduce 'a signal proportional to a separate digit of a multi-digitnumber. In this manner each phase detector is required to divide the 360of the sine wave into no more parts than the radix of the countingsystem used, which in the embodiment illustrated is ten.

The output signal from the phase detectors can be used in a variety ofdifferent ways to provide a visual display of the displacementinformation or to operate control equipment. By using a novel digitizingtube of the electron beam type, the displacement information is directlydigitized in a single element and the system is characterized by aninherent synchronization between the analog mechanical input and theelectrical digital output without reference to an accumulated count. Thedigital indication is therefore determined by the electrical phasedifference between the sine waves and the indication does not changewhen the equipment is again energized after being turned off.

It is accordingly a major object of this'invention to provide animproved position indicator for precisely measuring the displacement ofan object in space.

It is another object of this invention to provide a system utilizing aphase comparison between two continuous electrical signals for providingprecise measurements of distances -or angles of rotation.

Still another object of the invention is to provide a phase expansionsystem for more accurately indicating the exact electrical phasedisplacement between two continuous electrical signals.

A further major object of this-invention is to provide a system whichhas an output signal in a numeric or digital form for preciselyindicating the displacement of an object in space.

A still further object of this invention is to provide for selectivephase expansion of the signals in various channels with each channelproviding a single digit of a rnulti-digit number.

Another major feature of the present invention resides in the use of aresolver having different gains and combining their output signal toprovide the coarse digital indication.

Another object of the present invention is to make use of a resolvercapable of producing two output signals, one being a coarse outputsignal and the other being a fine output signal, with the coarse signalproviding the most significant digit in a multi-digit member and thefine output providing a lesser significant digit in a multidigit member.

Still another object of the invention is to provide a phase expansionsystem for both the coarse output and the fine output from the resolver.

A still further object of the invention is to provide phase expansionsystem capable of dividing a one" inch distance into ten thousand ormore distinct parts and which only requires a resolver constructionaccuracy of approximatelyfihe square root of one ten-thousandth of aninch.

These and other objects of the invention will become more fully apparentfrom the attached specification and claims and the appended drawingswherein:

FIGURE 1 is a block diagram of a phase expansion circuit;

FIGURE 2 is a schematic drawing of the electrical windings of one formof the resolver which can be used in the system according to theinvention;

FIGURE 3 is the circuit diagram of a phase detector circuit which may beused in the system;

FIGURE 4 is a diagrammatic view of a digitizing tube which may be usedin the present system;

FIGURE 5 is a :block diagram showing one arrangement for obtainingcoarse digital indications;

FIGURE 6 is a block diagram of a preferred form of the complete system;

FIGURE 7 is a block diagram of an alternative form of a phase expansioncircuit; and

FIGURE 8 is a circuit diagram of a flat phase network which may be usedin the system.

A complete system according to the present invention includes a numberof component parts each of which may be physically realized in manydifferent and varying forms determined by such conditions as the natureof the position to be resolved, the degree of resolution required, theresponse rate required, the form of output required and the operatingconditions imposed.

To clarify some of the terms used in the specification and claims thefollowing definitions are set forth:

Resolutiona measure of the smallness of an angle or linear distancewhich can be recognized.

Real-time operation-a term used to describe the rate of a process (dataprocessing) wherein said rate is equal to the rate of production of theraw data and is for all practical purposes coincident in time.

A system utilizing the basic principles of the present invention isillustrated in FIG. 1 and includes a resolver 20, an oscillator 22, andphase detector 24.

Resolver 20 may be of any suitable type and examples are disclosed inUnited States Patents Nos. 2,671,892 to Childs and 2,674,729 to Carter.Ordinarily such resolvers include electrical conductors on both a fixedelement and a movable element which are inductively and/ or capacitivelycoupled together. A source 22 of the electrical signals having constantfrequency and amplitude is connected to an input conductor on resolver20 and a output signal of the same frequency but displaced in phase byan amount proportional to the mechanical input angle is produced at anoutput terminal.

The output signal from resolver 20 is applied as one input to a phasediscriminator or detector 24 and the undelayed reference signal fromsource 22 is applied as the other input. Amplifier 26 may be used toprovide the proper amplitude of signal to detector 24.

A static D.-C. output signal is obtained from detector 24. The magnitudeof this signal is proportional to the phase difference between the twoinput signals applied to detector 24 and is applied as an input signalto a digitizing means 28.

High accuracy in any system comparing the phase displacement between twosine waves requires sine waves having very little distortion and thedifficulties encountered in the physical construction and the electricaloperation of the various circuit elements involved makes it impracticalto even consider the possibility of dividing the output signal from asingle phase detector into one hundred thousand uniform parts.

According to the present invention, the extremely high accuracy isobtained by phase expansion or 1nnltiplication of the phase angle basedon generation of harmonics by a non-linear device. Upon modulation of asignal of the form sin (wr+) by a non-linear device or frequencymultiplier 30 in FIGURE 1 whose output current may be expressed by aTaylor Series Expansion, the nth harmonic is obtained by the expansionof sin n(wt+0). This results in a term containing a constant coefiicientand sin Iz(wt+0).

Since sin n(wt|6):sin (nwt+n0) and 0 is the phase difference between theoutput signal from resolver and reference signal source 22, mixing thenth harmonic with the (/i |l)th harmonic will produce a signal having acomponent sin (wt+l10). This component when obtained from the signalsfrom multiplier and 32 at mixer 34 is applied to detector 36 anddigitizer 33 to produce the second most significant digit.

Further multiplication of the output signal from mixer 34, which is inthe form sin (wt-H10), by the same factor of It produces a signalrepresented by sin (nwt-l-n fl). By mixing this signal with the outputfrom frequency multiplier 32, the input signal to phase detector 44 issin (wt-H1 6). The output from phase detector 44 applied to digitizer 46therefore is proportional to the third most significant digit in thenumber,

Several different types of rotary and linear displacement resolvers canbe used in this system including goniometers, selsyns, slotted lines anda variety of printed circuits having one stationary and one movablepart. Each resolver can be made to yield a signal sin (wt-H1) where 0 isproportional to the displacement of the mova'ble element. This isclearly shown in the case of slotted balanced transmission lines havingno standing waves. The phase of the signal received by the movable probein the slot is compared with the phase at some fixed point. Other formsof resolvers make use of general equation sin (xy):sin x cos y-cos x siny.

In Patent No. 2,671,892 to Childs, the means for providing a 360 phaseshift of the output signal from the resolver for a mechanical rotationof only a few degrees is disclosed. Still another type of resolvercapable of dividing 360 of mechanical rotation into a large number ofparts is illustrated in FIGURE 2. This resolver consists of a drivercomponent which is ordinarily stationary and a movable or rotatablesensor component. The driver component consists of two continuouselectrical conductors 51, 52 geometrically lying in the same plane in acircular path whose distance from the center is periodic about aconstant radius. Conductors 51 and 52 have the same period of wave form.Conductor 5! is displaced with respect to conductor 52 by one quarter ofa period. Stated differently, conductor 51 is displaced by a phase angleof with respect to conductor 52. The radii of conductors 51 and 52 maybe different to eliminate overlapping.

If a common alternating voltage source drives a quadrature phasesplitting network whose output is such that conductor 51 is fed with avoltage 90 out of phase with respect to conductor 52, then the currentsthrough conductors 51 and 52'will be 90 out of phase in time at allpoints along their lengths.

If a third conductor 53 of similar geometrical configuration having thesame geometric periodicity is placed on top of conductors 51 and 52,voltages will be induced in conductor 53 by the alternating currents inconductors 5 and 52. The mutual inductances with respect to conductors51 and 52 will vary with the position of 53 to 51 and 53 to 52 and theE.M.F. in conductor 53 will therefore be a function of displacement,either angular or linear, as well as the magnitudes and phase (time) ofthe instantaneous currents in conductors 51 and 52.

The function which defines the manner in which the mutual inductancevaries With angle may be established by selection of a suitablegeometrical relationship be tween conductors. If the relationshipbetween conduc tor 53 (hereinafter referred to as 3) to conductors 51(hereinafter referred to as l) and 52 (hereinafter re ferred to as 2) isarranged such that for a given position, the mutual, inductance andhence the induced E.M.F. is related to the phase angle 0 in spacebetween conductor 3 and conductor 1 as follows:

E.M.F. 3.1 is the voltage induced in conductor 3 due to current inconductor 1. 3.2 is the voltage induced in conductor 3 due to current inconductor 2.

H H: are constants depending on geometry Where I I are the amplitudes ofthe currents an 1 :1

. (lz (lf then I(t dt -wI cos wt, j(1 (u -wI sin wt Since the inducedEMF. is related to the rate of change of the current.

Substituting the expresion for f(i and j([ in equation (3) 3.1+E.M.F.3.2:Hwl cos wt sin 0 +Hwl sin wt cos 0:Hwl (sin wt-i- 0) =3.6 S ace p(6) Each pole pair, however, represents 360 of electrical phase changeas the sensor component moves over the driver element. Consequently, theexistence of the pole pair further divides 3.6 by 360.

Therefore each degree of phase is equal to:

(Space) 3.6 (Electrical) 360 .01 of rotation of sensor component withrespect to the driver component.

If we define the gain of the resolver by Gain-G 4 where A6 is the changein angle in electrical degrees of the sensor and A is the change in theangle of the shaft position then the gain is equal to the number of polepairs. The angular gain of the resolver is consequently 100.

To retain the sense of direction of displacement in the output signal, adual or polyphase detector system is used for detectors 24, 36 and 44.An example of such a detector circuit is illustrated in FIGURE 3 whichcomprises essentially a pair of phase detector circuits which may be ofany conventional type connected to produce two output signals that are90 out of phase when the same input signals are used.

In the illustrated phase detector, coils 60 are center tapped and oneend of coils 62 is connected to the center tap. The input signals whosephase difference is to be measured are inductively coupled to therespective coils and the DC. voltage output obtained across resistors 64and 66 is proportional to the phase difference between the two inputsignals.

If reference signal E sin wt is compare-d with a signal E sin (wt+k0)from the resolver, then a voltage E will be generated of the form E sink0.

If the reference signal E sin wt is shifted 90 and injected into asecond phase detecting network and compared with signal E sin(wt-t-kfi).

E =E sin (k0+90)=E cos k6 the intelligence carrier E sin (wt-|-k0) inone phase detector, and E cos wt is com-pared with E sin (wt-Hm) in theother detector. The outputs of the detectors are fed to the deflectionplates of a cathode ray tube, one signal, E sin k6, on the horizontaldeflection plates and the other, E cos k6, on the vertical deflectionplates. In this manner a beam position is established whose angularposition is equal to k6, from a reference point.

Since 6 is continuously variable, k0 is an analogue quantity. The taskof digitizing this quantity is left to the digitizing means. It issuflicient to state here that the tube shown in FIGURE 4 permits therotation of the beam in discrete steps A; 360" per step. As the beamrotates in discrete steps, each step has associated with it, a uniquesignal which will be sampled for readout purposes.

The digitizer means may be any system of type which operates to providea change in digital indication in response to a change in the signallevel of the static DC. output signal from phase detector 26. Oneexample is il lustrated in FIGURE 11 of United States Patent No.2,685,082 to Beman and Caldwell. However, the digitizing means ispreferably of the type described in FIGURE 4, but may take other formsas desired. This quantitizing or analog to digital conversion isconveniently achieved by a novel cathode ray tube more fully describedand claimed in Serial No. 671,816 filed July 15, 1957 in the name ofSearle G. Nevius. The cathode ray tube includes the usual elements of anelectron gun including a heater 78, cathode 80, grid 82, high voltageelectrode 84 and focusing electrode 86 energized by a suitable powersource 88.

The input signal is applied to deflection plates 90 and 92 such that thebeam circularly scans a ten element target 94 of which only five areshown. Referring to the beam spot position at the target end of the tubethere are three fields affecting this position, two of these, the X andY displacement, position the spot in a circle by means of quadratureinput signals from the phase detectors. Inst below these fields are tenradially aligned deflection electrodes 96. Each of these electrodes isconnected to a corresponding target collector segment 94. Thesecollector segments have the property of emitting secondary electrons dueto the impact of the beam. The beam, impinging on a given target segment94, will cause the charge of that target segment to become positive byreason of the secondary emission from the target. The closed loop to thecorresponding deflection electrode 96 will attract the beam and cause itto be bent toward the deflection electrode. The beam will continue tostrike the given target segment 94 even to the point where the beam pathmoves directly opposite the adjacent deflection electrode 96. When themagnitudes of the quadrature input signals are such as to move the beamfrom one target segment to the next, a detent action results since thebeam was bent to a location directly opposite the adjacent deflectionelectrode. The step function or detent action acts the same wayregardless of the direction of progress of the electron beam.

The digitizer tube acts as a direct coupled follower of the resolverand, as such, is bi-directional. The maximum digitizing rate of a singletube is limited by the transit time of the electron beam plus the targetRC time constants.

To insure that the proper phase relationship exists between theinformation-carrying inputs to the phase dctectors of the variousdigitizer tubes, means are provided for the insertion of a fixed phaseshift on the above inputs to all digital places except the leastsignificant. When the digitized value in a particular digitizer tube isin the second half of its range, a retarding phase shift equal inmagnitude to one half of the shift required for a single digit change(in the next higher order digital place) is applied to theinformation-carrying input of the next higher order digital place. Thiswill prevent the next higher order digitizer tube from changing itsdigital indication before the next lower order tube changes from 9 to 0or 0 to 9.

A separate load circuit 100 associated with each target electrode 94produces a voltage output when the electron beam is associated with thatparticular electrode and thereby provides an output signal that is in adigital or non-continuous form even though the input is a continuousfunction. The output may be used to control conventional visual displaycircuits such as columns of neon bulbs, an electric typewriter, a tapeperforator or line printer. An example of a read-out circuit that may befed by load circuits 1100 and energize such equipment is described inSerial No. 271,825, filed February 15, 1952, in the name of W. D.Caldwell and assigned to the assignee of the present invention.

It is thus apparent that the digitizer produces a number of discreteindications equal to the radix of the counting system used. Since humanbeings are accustomed to use a counting system based on the radix 10, itis convenient to design the digitizer to produce an output consisting of10 distinct indications for the 360 of mechanical rotation of themovable element in resolver 20.

Since the resolver construction of FIGURE 2 produces 360 of electricalphase shift in the output signal as the sensor component mechanicallyrotates only of a revolution with respect to the driver component, eachpole pair will produce identical phase intelligence. To eliminate needfor an accumulative or integrating device indicating the total number ofpole pairs traversed, a second drive and sensor element may be connectedto the same resolver shaft to produce a coarse output signal in themanner described in Patent No. 2,671,892 or in other suitable fashion.For example, a driver and sensor similar to the 100 pole pair unitdescribed in connection with FIGURE 2 may be used. This similar set,however, contains either 99 or 101 pole pairs in its circuit. In accordance with the equation (7) given above, the mechanical gain of thissection of the resolver is 99 or 101 depending upon the number of polepairs used. By comparing the electrical phase angles of one set with thephase angle of the other as illustrated in FIGURE 5, a course indicationis obtained in the following manner.

The output signal from oscillator 120 is fed to the input winding ofsection 1 of resolver 122. The output signal from section 1 is then alsoused to power section 2 of resolver 122. The second section of theresolver operates upon the signal supplied from the first section togive an output which may be written sin (wt+6(n n (8) A digit which isproportional to the mechanical displacement of the movable element andaccordingly provides the most significant digit of a multi-digit numbermay be obtained by a circuit where n =n +1. This is obtained by having,say, 100 pole pairs on section 1 and, say, 99 pole pairs on section 2.Since section 2 has, in this case, one less pole pair than section 1 andbecause it is powered with the output of section 1 which has 100cyclical phase revolutions per turn of the input shaft, section 2 Willsubtract all but one cyclical phase revolution per single turn of theinput shaft. Therefore, the output from section 2 will be E sin(wt-t-G). This signal is supplied to the first order column phasedetector 1127, together with the reference signal E sin wt from theoscillator 12!). The output from the phase detector 127 is supplied to adigitizer 128 and corresponds to a 360 phase advancement for each singleturn of the input shaft.

The output signal E sin (wt-l-O) from section 2 of the resolver is alsosupplied to harmonic amplifier 129 Where it is multiplied by 10,producing the output E sin 10(wt+t9) The reference carrier E sin wt fromthe oscillator 120 is supplied to harmonic amplifier 130 where it ismultiplied by 9 providing the output E sin 9(wt). The output from the X9 multiplier (harmonic amplifier 130) and the output from the X 10multiplier (harmonic amplifier 129) are combined in mixer 131. Theoutput from mixer 131, may be Written E sin (WI-l-lOO). If this outputsignal is compared with the reference carrier E sin wt from theoscillator 120 in phase detector 132, the output from the detector willbe the phase angle 6 expanded by a factor of 10. This exampleillustrates the general method by which the phase angle is expanded by afactor of 10. The hundreds order column digit is obtained from theoutput signal E sin (wt-H000) of section 1 of the resolver 122 by meansof the multipliers and detectors of FIG. 1 as hereinbefore described andexplained. The expansion can be carried out by many differentarrangements of which FIG. is illustrated as a preferred form.

In FIGURE 6 differential resolver 150 is similar to the one shown inFIGURE 5 and has two sections one having an electromechanical gain of 99and the other having a mechanical gain of 100. Oscillator 152 near thecentre of the diagram is a constant frequency signal generator whoseoutput signal is fed through line 154 to power amplifier 156 and throughphase shifter 153 to power amplifier 160.

0 The signal output from amplifier 156 is fed to one induc tor ofsection 1 of the differential resolver which has a mechanical gain ofand the output from amplifier 160 which is 90 out of phase with theoutput from amplifier 156 is fed to the other inductor in section 1. Anincrement of shaft movement of the differential resolver provides at theoutput of section 1 on lead 162 a signal of the same frequency buthaving its phase displaced by one hundred times the mechanicaldisplacement of the removable resolver element. This signal is amplifiedby amplifier 164 and limited in limiter amplifier 166 and then fedthrough conductor 163 to power amplifier 170 and through phase shifting172 to power amplifier 174.

It should be understood that the actual wave form is not necessarily asine wave but is merely a form that can be expressed by a Taylor SeriesExpansion and that the terms sine and cosine are used to identify thetime phase position of the various signals rather than the exact shapeof their wave form. The output signals from power amplifiers 170 and 174are fed to section 2 of difIercntial resolver 150 which has a mechanicalgain of 99. By having phase shifter 158 advance the signal in itschannel by 90 and phase shifter 172 delaying the signal in its channelby 90, the differential resolver effectively subtracts the phase delaycaused by section 2 from the phase delay caused by section 1 therebyproviding an output signal on line 176 whose electrical phase is equalto the mechanical displacement angle of the movable element ondifferential resolver 150. This simplifies the circuit involved andprovides a more stable operation than is obtained by the system shown inFIGURE 5.

The signal on line 176 is accordingly called a coarse" indication signaland it is amplified by amplifier 178 and limiter amplifier 180. Oneoutput of amplifier 180 is fed through line 182 to polyphase detectorsections 184 and 186. A second input to phase detector section 184 is obtained from the output of power amplifier 16% through conductor 188. Thesecond input to phase detector section 186 is obtained from the outputof power amplifier 156 through conductor 190. This phase detector is ofthe type illustrated in FIGURE 3 and provides an input signal to thedigitizer tube 192 proportional to the most significant digit in amulti-digit member which represents the mechanical phase position of themovable element of differential resolver 150. As discussed in connectionwith FIGURES l and 2 the exact wave forms applied to phase detectors 18and 186 are not critical since the digitizer tube only produces anoutput signal that is accurate to the nearest 36 or one-tenth of 360.

A second output from limiter amplifier 130 is connected throughconductor 194 to a tenth harmonic amplifier 196 whose output is appliedas one input signal to mixer 198. The second input signal is obtainedfrom a ninth harmonic amplifier 260 whose output is applied throughconductor 202 as the second input to mixer 193. The output signal frommixer 198 is then applied as one input to phase detectors 2-04 and 206With the other input to each phase detector obtained from poweramplifiers 160 and 156 through conductors 188 and respectively.

The mathematical analysis of the phase expansion and the digitizing ofthe second most significant digit in the coarse indication as given inconnection with FIGURE 5 clearly illustrates the principles of phaseexpansion and the methods of obtaining a decade system. The samephilosophy applies to the system arrangement shown in FIG- URE 6 but theexact equations are slightly modified because of the circuit connectionsbetween the output of section 1 of resolver 150 and the input to section2.

The third most significant digit in the multidigit memher is obtained bytaking the output signal from section 1 of differential resolver 150 asamplified by amplifiers 164 and 166 and applying it directly as oneinput to phase detector sections 240 and 24-2. The other input to eachphase detector section is the same as used in all of the 9 phasedetectors and is applied fro-m power amplifiers 160 and 156.

The fourth most significant digit is obtained from conductor 243carrying the third most significant digit signal from limiter amplifier166 and is multiplied in harmonic amplifier 244 where the tenth harmonicis applied as one input to mixer 245. The other input to mixer 248 isthe ninth harmonic of the reference signal obtained from amplifier 200thereby causing the output signal of the mixer to have its phase shiftedby a factor of one thousand times the mechanical angular displacement.This signal is applied to phase detectors 247 and 246 to provide thefourth most significant digit at the output of digitizer 248. i The sameoutput signal from mixer 245 is applied to harmonic amplifier 250 whichproduces a tenth harmonic to be fed to mixer 252. The second input tomixer 252 is also obtained from harmonic amplifier 200 and the phase ofthe output signal from mixer 252 has been shifted by a factor of tenthousand. This signal is applied to phase detectors 254 and 256 whichsupply the fifth most significant digit in a multi-di git number.

There has thus been described a system which is capable of reliableoperation and which will divide the 360 of a circle of revolution into100,000 parts. Actual experimental mode'ls have been made which produce200,000

digital counts for one revolution.

The systems described thus far employ heterodyning techniques to providethe phase multiplied signals to the phase detector at the same frequencyas the reference carrier frequency. In FIGURE 7 there is shown a systemwherein the reference carrier is multiplied by the same factor as theintelligence or phase shifted carrier so that the inputs to the phasedetector will be at the same frequency. An oscillator 257 supplies areference carrier frequency signal to resolver 258 via an inputconductor, An output signal is obtained from the resolver having thesame frequency but displaced in phase by an amount proportional to themechanical input angle 0. The output is applied via amplifier 259 as oneinput to a phase discriminator or detector 260 and the undelayedreference signal from source 257 is applied as the other input. NetworkA may be used to provide the proper correction for time of transmissionthrough the system as will hereinafter be explained and discussed. A DC.amplitude output is obtained from detector 260. The magnitude of thissignal is proportional to the phase difference between the two inputsignals applied to the detector 260 and is app-lied as an input signalto a digitizing means 261. The phase shifted output from the resolvermay be represented as E sin (wt-F) and is multiplied by frequencymultiplier 262 to give E sin 10 (wt-+0). The undelayed reference carrieris multiplied by frequency multiplier 263 to give E sin 10(wt) Theoutput signals obtained from multiplier 262 and multiplier 263 areapplied to detector 264 and digitizer 265 to produce the second mostsignificant digit. Further multiplication of the output signal frommultiplier 266 by a factor of 10 produces a signal represented by E sin100(wt-l-0). The output from multiplier 267 is similarly muliplied by afactor of 10 to give the reference carrier represented by E sin 100(wt).The outputs from multipliers 266 and 267 are applied to the inputs ofphase .detector 268. The output from phase detector 268 applied todigitizer 269 therefore is proportional to the third most significantdigit in the number.

In each of the systems described it may, of course, be desirable torecord the position of the resolver while its movable element is inmotion. If the transmission circuits employed in the system exhibitvarying phase shift with frequency, there will be a velocity errorintroduced whenever a reading is taken while the resolver is in motion.The rate of change of phase shift indicates directly the velocity of themovable element in the resolver with respect to the fixed element as aDoppler frequency. A

10 novel four terminal network disclosed in my co-pending applicationS.N. 693,979, filed November 1, 1957, now Patent No. 2,965,860,incorporates phase correcting sections having positive phase shifts withchanges in freqnecy which neutralize the negative phase shifts inconventional filter sections to provide a flat phase response over thedesired pass band. Referring to FIGURE 8, the first sec-' tion of thisnetwork comprises a primary circuit which is over coupled to a secondarycircuit which is in turn connected to a power dissipating load.Considering the current flow in the primary circuit alone, at resonancethe lagging current through inductance 270 and the leading currentthrough capacitance 271 are equal and out of phase thereby neutralizingeach other. The phase of the output voltage signal will then lead thenetwork input current signal when the frequency is less than theresonant frequency and will lag when the frequency is greater than theresonant frequency. Secondary circuit 272 may be similar to or evenidentical with primary circuit 273. When the coefficient of couplingexceeds critical coupling the relative phase of voltage across thesecondary capacitance 274 as a function of frequency will exhibit aphase lead for frequencies less than resonant frequency, zero phaseshift at the resonant frequency, and a lag for frequencies above theresonant frequency. The relative phase shift (as contrasted withrelative phase of voltage) for different frequencies of the pass band isalways negative and does not reverse. This is a common characteristicfor nearly all conventional filter circuits. Primary circuit 273exhibits an entirely different phase behavior as regards the relativephase shift for different frequencies of the pass band depending uponthe degree of coupling. When the primary and secondray circuits arecritically coupled, near the resonant frequency the relative phase shiftis zero. By increasing the coupling so that primary circuit 273 andsecondary circuit 272 are over coupled, the relative phase shift will bepositive. Furthermore, the degree of relative positive phase shift issubstantially directed proportional to the degree of over coupling andby making the degree of over-couple large the positive phase shift canbe made quite large. The positive phase shift is due principally to thepower drawn by secondary circuit 272 from circuit 273. By varyingresistive load 275 which draws power from the secondary circuit thefrequency parameters of the network may be altered. A small couplingcapacitor 276 may optionally be used. The input current and the outputvoltage appear at terminal 277 as the output signal from the network iseffectively taken from the primary circuit. A novel four terminalnetwork having flat phase characteristics can be constructed bycombining a conventional filter having a negative relative phase versusfrequency as first described with a filter section of the type having apositive relative phase versus frequency as last described. One of thefilter sections may be connected in series with the line by connectionto terminal 278 while the other may be effectively across the line byconnection to terminal 277. By controlling the degree of over couplingbetween the primary and secondary circuits, a four terminal network canbe constructed having a zero relative phase shift for a band offrequencies the center of which is substantially the reference carrierfrequency of the phase measuring system. Moreover, the amplitude of thesignal from the combined sections can also be controlled to besubstantially constant over the same band width. Interstage coupling ofthe various elements of theresolver digitizing or phase measuring systemof the present invention may be affected by the fiat phase four terminalnetworks as just described and as shown at the points marked A in FIG.7. Velocity errors may thus be cancelled out out and real-timedigitization of the resolvers position may be accomplished while theresolver is in motion. Other sources of phase versus frequencydistortion may also be cancelled out by introduction of the flat phasenetwork into appropriate points in the phase measuring system.References to resolvers in the foregoing paragraphs should be consideredto include flat phase shifting networks having selectable terminals tointroduce fixed incremental phase shifts into the system. Suchpresettable networks may be algebraically additive to the output from anangular resolver. This will provide a convenient means for establishinga desired (zero) reference point from which the shaft rotation may bemeasured. A presettable reference point may be especially desirable inthe present invention in that it does not depend upon countingtechniques to indicate the relative position of the input shaft. Thatis, the mechanical input to the resolver shaft may be established whilethe electronic system is turned off and the correct position of theshaft will be indicated when the power is turned on.

It is to be understood that linear resolvers can be uscc equally well,and with carefully constructed resolvers, the phase expansion can becarried on considerably further. However, the accuracy of the windingson the resolver must be of the same order as the phase expansion andwith a -inch resolver winding, the conductor patterns must be locatedwith an accuracy of th of an inch. By using fine windings or resolvcsrshaving significant mechanical gains, the acuracy required for individualconductor positions is only the square root of th of an inch because theoutput signal is a statistical average over several individualconductors.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. A system for measuring the phase difference between two electricalsignals comprising a first signal channel having a phase detectorresponsive to said electrical signals to generate an Output signalproportional to the phase difference between said electrical signals; asecond channel containing means for multiplying the frequency of atleast one of said electrical signals, means in said second channelresponsive to the other of said electrical signals and to saidmultiplied electrical signal to generate a D.-C. voltage proportional tothe phase difference therebetween and, means responsive to said DC.voltage, in conjunction with said output signal from said phasedetector, to provide an accurate indication of the phase differencebetween said electrical signals.

2. In a system for indicating the phase difference between twocontinuously recurring electrical signals, means for connecting saidsignals to a first phase detector, a second phase detector, meansmultiplying the frequency of said signals to multiply the phasedifference between said signals, means connecting the multiplied signalsto said second phase detector, and means responsive to the outputs ofboth of said phase detectors for indicating the phase difference betweensaid signals.

3. In a system for indicating the phase between two electrical signals,means for connecting said signals to a first phase detector, meansmultiplying the frequency of one of said signals by a first factor tomultiply the phase difference between said signals, means multiplyingthe frequency of the other of said signals by a second factor, mixermeans for heterodyning the multiplied signals to provide a differencefrequency output, means connecting the multiplied signals to said mixermeans, a second phase detector, means connecting one of said electricalsignals to said second phase detector, means connecting the differencefrequency output from said mixer to said .second phase detector, andmeans responsive to the out- 12 puts of both said phase detectors forindicating the phase difference between said electrical signals.

4. The method of producing manifestations in the form of digits of amulti-digit number which is proportional to the phase difference betweentwo electrical signals comprising: combining said two electrical signalsin a first phase detector to produce a manifestation proportional to onedigit of said multi-digit number, multiplying the frequency of one ofthe electrical signals, generating a comparison signal having apredetermined frequency relationship with the two electrical signals andhaving the same frequency as the multiplied frequency, combining themultiplied signal and the comparison signal in a second phase detectorto produce a manifestation proportional to a second digit of saidmulti-digit number.

5. The method of producing manifestations in the form of d gits of amulti-digit number which is proportional to the phase difference betweentwo continuously recurring electrical signals comprising: combining saidtwo electrical signals in a first phase detector to produce amanifestation proportional to one digit of said multi-digit number,multiplying the frequency of the electrical signals, and combining themultiplied signal frequencies in a second phase detector to produce amanifestation proportional to a second digit of said multi-digit number.

6. The method of producing manifestations in the form of digits of amulti-digit number which is proportional to the phase difference betweentwo continuously recurring electrical signals comprising: combining saidtwo electrical signals in a first phase detector to produce amanifestation proportional to one digit of said multi-digit number.multiplying the frequency of one of the two electrical signals by afirst factor, multiplying the frequency of the other of the twoelectrical signals by a second factor, combining the multipliedelectrical signals in a mixer, combining the output from the mixer withone of the electrical signals supplied to the first phase detector in asecond phase detector to produce a manifestation proportional to asecond digit of said multi-digit number.

7. In combination, a source of a reference signal at a predeterminedfrequency, a pair of signal channels connected with said source, phaseshifting means in one of said signal channels for effecting a phaseshift of said reference signal by an amount proportional to a parameterto be measured, first multiplying means connected with the output signalof one of said channels for multiplying the frequency of the phaseshifted signal in said one channel by a first factor, second multiplyingmeans connected with the output signal of the other of said chan nelsfor multiplying the frequency of the signal in said other channel by asecond factor, mixer means connected to said first and secondmultiplying means to combine said multiplied signals and thereby providean output signal having the same frequency as said reference signalfrequency, phase detector means for comparing the phase of the outputsignal from said mixer means and the refcrencc signal, and meansresponsive to the output of said detector means for digitizing saidphase difference.

8. in a phase measuring system, a source of a reference signal at apredetermined frequency, phase shifting means for effecting a phaseshift of said reference signal by an amount to be measured, a pluralityof channels connected to the output of said phase shifting means, afirst phase detector in one of said channels, the output of which is afirst signal voltage proportional to a first digit, phase expansionmeans in another of said channels, the output of which is a multiple ofthe phase shifted signal from the output of said phase shifting means,and a second phase detector, the output of which is a second signalvoltage proportional to a second digit, said first digit and said seconddigit being separate digits of a plural order number.

9. In a phase measuring system as defined in claim 8 having meansconnecting said reference signal to said first phase detector, means fordigitizing said first signal voltage to produce the highest order digit,:1 first frequency multiplier connected to said second phase detector,means for supplying a comparison signal to said second phase detectorhaving a predetermined frequency relationship with the reference signaland of the same frequency as the multiplied frequency output from thefirst frequency multiplier, means for digitizing said second signalvoltage to produce the second highest order digit, a third frequencymultiplier and a third phase detector in a third of said plurality ofchannels, means for supplying a comparison signal to said third phasedetector having a predetermined frequency relationship with thereference signal and of the same frequency as the multiplied frequencyoutput from the second frequency multiplier and means for digitizing theoutput of said third phase detector to produce the third highest orderdigit.

References Cited by the Examiner WALTER L. CARLSON, Primary Examiner.

RUDOLPH V. ROLINEC, Examiner.

A. E. RICHMOND, P. F. WILLIE,

Assistant Examiners.

1. A SYSTEM FOR MEASURING THE PHASE DIFFERENCE BETWEEN TWO ELECTRICALSIGNALS COMPRISING A FIRST SIGNAL CHANNEL HAVING A PHASE DETECTORRESPONSIVE TO SAID ELECTRICAL SIGNALS TO GENERATE AN OUTPUT SIGNALPROPORTIONAL TO THE PHASE DIFFERENCE BETWEEN SAID ELECTRICAL SIGNALS; ASECOND CHANNEL CONTAINING MEANS FOR MULTIPLYING THE FREQUENCY OF ATLEAST ONE OF SAID ELECTRICAL SIGNALS, MEANS IN SAID SECOND CHANNELRESPONSIVE TO THE OTHER OF SAID ELECTRICAL SIGNALS AND TO SAIDMULTIPLIED ELECTRICAL SIGNAL TO GENERATE A D.-C. VOLTAGE PROPORTIONAL TOTHE PHASE DIFFERENCE THEREBETWEEN AND, MEANS RESPONSIVE TO SAID D.-C.VOLTAGE, IN CONJUNCTION WITH SAID OUTPUT SIGNAL FROM SAID PHASEDETECTOR, TO PROVIDE AN ACCURATE INDICATION OF THE PHASE DIFFERENCEBETWEEN SAID ELECTRICAL SIGNALS.